1. Field of the Invention
The present invention relates to a manufacturing method of a display device, particularly, a liquid crystal display device. The invention relates to a manufacturing method of a display device, particularly, a liquid crystal display device having high reliability and satisfactory productivity.
2. Description of the Related Art
A liquid crystal display device includes a TFT substrate having pixel electrodes, thin film transistors (TFT), etc. formed thereon in a matrix form, and a counter electrode opposing the TFT substrate and having color filters, etc. formed at positions corresponding to the pixel electrodes of the TFT substrate. Liquid crystals are put between the TFT substrate and the counter substrate. The liquid crystal display device controls light transmittance for each pixel by using liquid crystal molecules to form images.
Since a TFT substrate includes scanning lines, video signal lines, TFTs, etc. formed thereon, the surface of the TFT substrate is uneven. Unevenness of the surface of the TFT substrate will bring about variations in thickness of a liquid crystal layer put between the TFT substrate and the counter substrate and thus light leakage will occur at some places, resulting in decrease in contrast of the screen.
To prevent such a drawback, about 2 μm-organic passivation film is formed over the TFT, etc. to planarize the boundary to the liquid crystals and pixel electrodes, etc. are formed thereon. To connect the pixel electrode to the source of the TFT the organic passivation film needs to be formed with a through hole. Using a photosensitive resin for the organic passivation film allows for direct exposure to the resin and development without using a resist. Thus the process can be simplified.
A method of forming the organic passivation film using such a photosensitive resin includes a technique as disclosed in JP-A-2010-26460. This patent document describes a method of forming an organic film by using a positive photosensitive composition. Further, JP-A-2006-235134 describes a method of forming through holes different in taper angle by one shot photolithography using a photomask having a phase shift effect.